i dk i'm on debian stable but:
* tried support@quakelive.com?
* if you've got nvidia adapter, are you using nvidia proprietary drivers? (because u should)
* got compiz and other GPU intensive stuff turned off?

Yes to all..

okay, then what about firefox version... is it 3.6?
what about reinstalling ubuntu?
try a Long Term Support version of ubuntu instead of 11.04?

hehe.. i really hate having to spend time on reinstalling trying differetnt versions etc.. i might give it a go sometime. . i was hoping somebody knows this problem and how to fix this ± )

tried:
r_customheight y-res
r_customwidth x-res
r_mode -1 (custom reso)

OR

r_mode -2 (desktop reso)

OR

r_inbrowsermode 9
r_nofastrestart 0

fidding with these settings? it may be something stupid.

have you tried deleting repconfig.cfg and qzconfig.cfg and autoexec.cfg and going to game settings and clicking on reset to defaults?

edit: also have u disabled compiz? i'm not sure that that would affect the crashing but MAYBE. (plus no one should be running compositing (aero,compiz, etc) software while playing 3d accelerated games. i don't think.)

i was hoping somebody knows this problem and how to fix this

Desktop resolution resets to 800x600 because of game crash.

i use ubuntu 11.04 and i don't have this bug.

what r_mode do you use? i had to use r_mode "actualmode" (23, 1920x1080) to get things to work, -2 (desktop resolution) failed for me.
on the other hand, you see that i play in my native/desktop resolution anyway, so i doubt i can be of much help here .)

Whenever I quit a game..

(c) brumu

Maybe error.log can give you any hints why ql crashes? Found in $HOME/.quakelive/quakelive/home/baseq3